Some love to nbviewer first page

remove broken link, update some other,
inprove css layout for form when windo is not wide
resize images to be at maximum the size they will be on screen
crush png 1.7 -> 1.3 Mb
remove unused thumbs
Merge pull request #110 from Carreau/some-love

Some love to nbviewer front page
Only set theme if not None, coerce nvisits to str
Get rid of cookies
Merge pull request #112 from rgbkrk/cookie_fix

Get rid of cookies to set theme.
overwrite bootstrap pre-background color
Merge pull request #115 from Carreau/master

overwrite bootstrap pre-background color
update requirement
Merge pull request #116 from Carreau/clean-requirement

update requirement
make nbviewer a package

use tornado to serve

works enough to start committing, but still some work to do
ignore some files
move templates and static into package dir
/url[s]/url work now

GitHub blob/tree urls are redirected
py3 compat
add memcache support, and use gen.coroutine
update requirements
remove unused js, less, img